The present invention relates to a new, economical, very efficient process for generating chlorine dioxide.
Inasmuch as chlorine dioxide is of considerable commercial importance in the fields of pulp bleaching, water purification, fat bleaching, removal of phenols from industrial wastes, textile bleaching, and the like, it is very desirable to have a process by which it can be economically generated.
One means for the generation of chlorine dioxide is by way of reaction of a chlorate, a chloride, and sulfuric acid. The reactions which occur are exemplified below, wherein, for the sake of illustration, the chlorate used is sodium chlorate and the chloride used in sodium chloride EQU (1) NaClO.sub.3 + NaCl + H.sub.2 SO.sub.4 .fwdarw. ClO.sub.2 + 1/2 Cl.sub.2 + Na.sub.2 SO.sub.4 + H.sub.2 O EQU (2) naClO.sub.3 + 5NaCl + 3H.sub.2 SO.sub.4 .fwdarw. 3Cl.sub.2 + 3 Na.sub.2 SO.sub.4 + 3H.sub.2 O.
this technique for chlorine dioxide production is used on a commercial scale, with the reactants continuously being fed into a reaction vessel and the chlorine and chlorine dioxide produced continuously being removed from the reaction vessel.
Another means for the generation of chlorine dioxide is by the reaction of a chlorate with hydrochloric acid. The reactions which occur are exemplified below, wherein, for the sake of illustration the chlorate used is sodium chlorate. EQU (1a) 2 NaClO.sub.3 + 4 HCl .fwdarw. 2 ClO.sub.2 + 2 NaCl + 2 H.sub.2 O EQU (2a) NaClO.sub.3 + 6 HCl .fwdarw. 3 Cl.sub.2 + NaCl + 3 H.sub.2 O.
typically, in such processes, the chlorine, chlorine dioxide and water produced are removed in the vapor state and the alkali metal salt is removed from the reaction solution by crystallization.
Various processes and systems have been employed for the generation of chlorine dioxide, chlorine, and an alkali metal salt based in general on the reactions shown in the above equations. Such systems include for example, systems comprising a multiplicity of generators operating in cascade flow (U.S. Pat. No. 3,446,584, to W. A. Fuller) or a combination of a poly-zoned apparatus or plural apparatuses in which various distinct chemical and/or physical operations have been separated into chlorine dioxide generation, water evaporation, by-product salt crystallization, and reactant introduction into the system (U.S. Pat. No. 3,516,790, June 23, 1970, U.S. Pat. No. 3,341,288, Partridge, Sept. 12, 1967).
More recently, it has been proposed to provide for the generation of chlorine dioxide, chlorine, and an alkali metal salt in a single reaction vessel. Thus, for example, in U.S. Pat. No. 3,816,077, Fuller et al., June 11, 1974, there is disclosed a system wherein the generation of chlorine dioxide and chlorine, the evaporation of water, and crystallization of an alkali metal salt, are effected in a single reaction vessel. Although substantial improvement in efficiency is achieved in the combining of these processes into a single reaction vessel, the system requires external conduits, pump, and heating apparatus for the mixing, heating, circulating and recycling of the reaction mixture. It will be appreciated by those skilled in the art that still further improvements are desirable to provide a system wherein a single process vessel is employed for the mixing and temperature control of reactants, the generation of chlorine dioxide, evaporation of water, and the crystallization of alkali metal salt, as well as the continuous and efficient circulation and re-circulation of reaction mixture.